Resumo

Bacterial infectious diseases represent a risk to world population and have been responsible for high morbidity and mortality through the times. This health public problem has been much more serious in the last decades with the increase in the prevalence of infections caused by multi-drug resistant strains. So, the looking for new antimicrobial agents and/or new compounds with ability of potentiate the antimicrobial activity of old antibiotics against multi-drug resistant bacteria has been considered an important area of research. The specie Lippia origanoides H.B.K. (Verbenaceae) is a medicinal plant known locally as alecrim-do-campo. It has been used as culinary seasoning and in traditional medicine as remedy for gastrointestinal disorders and respiratory diseases treatment. At the present study, the Lippia origanoides H.B.K. dichloromethane fraction (LODCM) was tested for their antimicrobial activity alone or in combination with conventional antibiotics used in the treatment of infectious diseases caused by Staphylococcus aureus and Escherichia coli. The natural products didn’t show antimicrobial activity against multi-drug resistant strains at the clinically significant concentrations tested, once the minimal inhibitory concentration (MIC) value obtained was ≥1024 µg/mL. However, a synergistic effect was verified when LODCM was used in association with Neomycin, Amikacin and Tetracycline for methicillin resistant S. aureus (MRSA) strain. The MIC values for Neomycin, Amikacin and Tetracyclin alone were 2500, 787.5 and 78.1 µg/mL, respectively. These were reduced to 39.1, 39.1 and 19.5 µg/mL, respectively, when they were associated with the LODCM against MRSA strain. A similar synergism was observed when the natural products were changed for chlorpromazine, a drug able to inhibit efflux pumps, suggesting the involvement of resistance mediated by efflux system. On other hand the LODCM didn´t show synergistic effect when used in association with the same antibiotics against E. coli. These results indicate that L. origanoides H.B.K. hexane fraction could become a promising natural product how a modifier agent of antibiotic resistance in S.aureus.